Identification of ions Flashcards
A flame test can be used to…
identify positive ions.
Lithium
crimson
Sodium
yellow
Potassium
lilac
Calcium
red
Barium
green
Reaction with…
sodium hydroxide can help us to identify some positive ions.
What ions can be identified using sodium hydroxide?
- aluminium
- magnesium
- calcium
- copper (ll)
- iron (ll)
- iron (lll)
Aluminium, magnesium and calcium reacting with sodium hydroxide form…
white precipitate.
To identify aluminium precipitate…
we add an excess of sodium hydroxide and the white precipitate will dissolve.
Copper (ll)
Form blue precipitate
Iron (ll)
Form green precipitate
Iron (lll)
Form brown precipitate.
Magnesium in a flame test
Has no colour.
Carbonate and dilute acid produces
carbon dioxide which creates a white precipitate in lime water, turning it cloudy.
Test for halide ions
- add dilute nitric acid to the sample
- add dilute silver nitrate solution
- halide ions will produce a coloured precipitate
Chloride ions
White precipitate
Bromide ions
Cream precipitate
Iodide ions
Yellow precipitate
Test for sulfates
- add dilute hydrochloric acid or nitric acid
- add barium chloride solution
- sulfate ions form a white precipitate
Why is imporatant to first add hydrochloric or nitric acid?
This removes carbonate ions that would form a precipitate with barium ions.
The white precipitate in a test for sulfates is…
insoluble salt barium sulfate BaSO4